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α 2A ‐Adrenergic receptors are present in μ‐opioid receptor containing neurons in rat medial nucleus tractus solitarius
Author(s) -
Glass Michael J.,
Pickel Virginia M.
Publication year - 2001
Publication title -
synapse
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.809
H-Index - 106
eISSN - 1098-2396
pISSN - 0887-4476
DOI - 10.1002/syn.10036
Subject(s) - axon , μ opioid receptor , receptor , nucleus , neuroscience , agonist , biology , solitary nucleus , alpha (finance) , medicine , chemistry , endocrinology , construct validity , nursing , patient satisfaction
Agonists of the alpha‐2A‐adrenergic‐ (α 2A ‐AR) and the μ‐opioid‐receptor (μOR) jointly affect autonomic functions that are also disregulated in animals undergoing withdrawal from chronic administration of the μOR agonist morphine. Cardiovascular and gastrointestinal reflexes are mediated, in part, by the medial nucleus of the solitary tract (mNTS) at caudal (cNTS) and intermediate (iNTS) subregions. Together, this evidence suggests that α 2A ‐AR and μOR may be colocalized within many of the same neuronal profiles in both the intermediate and caudal mNTS. In order to examine whether α 2A ‐AR and μOR are present within common somata, dendrites, or axon terminals in the mNTS, we used electron microscopic immunocytochemistry for the detection of antisera against each receptor at intermediate and caudal levels of this brain region. Most of the dually labeled profiles were somata and dendrites. Of all dual‐labeled profiles in the iNTS 49% were somata and were 47% dendrites, whereas in the cNTS 61% were somata and 32% were dendrites. Within dual‐labeled profiles, the intracellular distribution of α 2A ‐AR and μOR differed. μOR was more frequently associated with the plasmalemma, whereas α 2A ‐AR was often affiliated with vesicular organelles. Few axon terminals, and even fewer glia, contained both markers. We also frequently observed single‐labeled α 2A ‐AR glia that apposed exclusively μOR‐containing dendrites or axon terminals. These findings indicate that somata and dendrites contain functional sites for convergent μOR and α 2A ‐AR activation. In addition, each receptor is positioned for involvement in intercellular signaling between apposed neurons and glia. Activation of α 2A ‐AR on μOR‐containing somata or dendrites, or on glia apposed to μOR‐containing neurons, may help to account for the efficacy of α 2A ‐AR agonists in relieving some of the autonomic symptoms of opiate withdrawal. Synapse 43:208–218, 2002. © 2002 Wiley‐Liss, Inc.